Internal combustion engines are known that may be operated optionally with a liquid auto gas (Liquefied Petroleum Gas; LPG), below known as LPG fuel, or a compressed natural gas (Compressed Natural Gas; CNG), known below as CNG fuel. Such internal combustion engines comprise a combustion engine, an LPG tank for storing the LPG fuel, and a CNG tank for storing the CNG fuel. Because at least one of said types of fuel is available in many countries, a supply of fuel for the corresponding internal combustion engine can be widely assured. Such an internal combustion engine is known from CN 204 877 718 U, for example.
However, the inventors herein have recognized issues with the above configurations. In combustion engines operating with LPG as fuel, LPG may be compressed in tanks in a liquid aggregate form. Upon release from the tank, LPG may be converted to a gas aggregate form under atmospheric pressure and normal ambient temperatures. In combustion engines capable of operating with either a CNG fuel or an LPG fuel with a single common fuel rail (also referred to herein as a distributor), it is possible to make a switch from an LPG fuel to a CNG fuel and vice versa, wherein CNG fuel is typically stored in CNG tanks in a gas aggregate form. During operations of the internal combustion engine, gas pressures and temperatures may vary considerably in the fuel distributor, and therefore the aggregate state of the respective fuels in the fuel distributor may be unknown and vary significantly depending on the operating conditions at the time of transition between the fuels. Thus, during operation of engines including both a CNG and an LPG fuel supply, mixing of different fuels with different aggregate states in the fuel distributor may occur, adversely affecting the supply of fuel to the internal combustion engine. Further, such a mixing of different fuels in different aggregate states may not only be poorly controllable, but may also further undesirably allow for a transiently unknown supply of fuel to the internal combustion engine.
Additionally, in combustion engines operating with LPG as fuel, hot start of a vehicle (e.g. engine startup when outside temperatures are hot) may not be instantaneous due to vaporization of the LPG in the fuel rail whilst the engine is stopped. Furthermore, engines operating with LPG as fuel, when the combustion engine and therefore the fuel supply is turned off, the LPG present in the fuel lines may switch into a gas aggregate state, necessitating a need for maintaining high pressure in the LPG fuel upstream of a high pressure pump to prevent fuel vaporization. Such fuel vaporization may make an engine restart difficult and delayed.
The inventors herein have recognized the above issues and provide an approach to at least partly address the issues. In one example, an engine system comprises a combustion engine with direct injection, an LPG tank for storing a LPG fuel, a CNG tank for storing a CNG fuel, an electrically controlled gas switching valve, a high-pressure pump connected between the LPG tank and the gas switching valve, a pressure-limiting valve connected between the CNG tank and the gas switching valve, a fuel distributor configured to be supplied with fuel via the gas switching valve, an LPG injection valve and a CNG injection valve per cylinder of the internal combustion engine, wherein the LPG injection valves and the CNG injection valves are configured to be supplied with fuel via the fuel distributor, and a controller to control the gas switching valve depending on an aggregate state of fuel disposed in the fuel distributor.
According to the example configuration described above, the switch between the respective fuels may be a consequence of the pressure and temperature existent in the fuel distributor and further, the method of switching from LPG to CNG and vice versa with the use of separate fuel injectors for both CNG and LPG, ensures that the two types of fuel with different aggregate states do not get mixed in the fuel distributor. Further, to increase the power of the internal combustion engine, the compression ratio of the cylinders may be increased without knocking occurring. The selective direct injection of LPG fuel and CNG fuel is controlled by the control and/or regulating electronics and the gas switching valve. The selective supply of LPG fuel or CNG fuel enables starting of the internal combustion engine under virtually any temperature conditions. Further, the availability of the additional CNG fuel with separate CNG injection valves, the hot starting problem connected with an LPG fuel supply may be reduced, for example the gaseous LPG fuel that could not be injected via the LPG injection valves may now be injected via the CNG injection valves during engine startup. In addition, a high pressure in the LPG fuel upstream of the high-pressure pump is not necessary, because the combustion engine can also be operated with a gaseous fuel, such as the CNG fuel for example. Furthermore, a reduction of CO2 emissions may be achieved by the use of LPG fuel and CNG fuel as described herein compared to the conventional use of gasoline. Furthermore, the internal combustion engine according to the disclosure can be operated using less expensive fuels.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.